Based upon the psychiatric basic documentation, the incidence of aggressive behaviour before admission and during hospitalisation in a psychiatric hospital was investigated for a six-year period from 1989 through 1994. Aggressive behaviour was found in 8.3% of the patients before admission and in 2.7% during hospitalisation. Injuries to other persons were relatively more frequent in patients with social disorders, mental retardation, dementia and schizophrenic psychoses. The relative risk was increased especially in patients who had injured other persons prior to admission. Considering only the included variables, prediction of aggressive behaviour is not possible with sufficient certainty.